Telomerase is a ribonucleoprotein that catalyzes the addition of telomeric repeats to the ends of telomeres. Telomeres are long stretches of repeated sequences that cap the ends of chromosomes. In humans, telomeres are typically 7-10 kb in length and comprise multiple repeats. Telomerase is not expressed in most adult cells, and telomere length decreases with successive rounds of replication.
Telomerase acts as reverse transcriptase in the elongation of telomeres, which prevent the loss of telomeres due to the end replication problems. Without telomerase the telomeres are shortened at each cell division which leads to senescence, apoptosis and cell death caused by chromosome instability. Telomerase is inactive in somatic cells but active in 90% of cancer cells, where telomerase is reactivated. Although telomerase activation may be dangerous, because it can mimic the cancer development process, telomerase enhancing agents may be theoretically applicable as anti-aging agents and clinically useful in certain medical conditions. In contrast, telomerase inhibitors may be useful to fight cancer. Cancer and aging are closely inter-related: Interventions that protect against cancer can lead to premature aging while immortalization of cells is required in the formation of malignant cancer cells. Despite the theoretical risk of activation of carcinogenesis, activation of telomerase may lead to reduced rate of aging.
The assessment of the telomere length is important in the understanding of biological and clinical significance of the telomere. The telomere length serves as a useful indicator in the study of the chromosomal stability, telomerase activity and/or expression, proliferative capacity and aging process of the cells. The clinical value of telomeres can be demonstrated in its importance in cancer, premature aging syndrome or segmental progeria; genetic anomalies, diseases resulting from chromosomal instability, such as Bloom syndrome (a rare inherited disorder characterized by a high frequency of breaks and rearrangements in an affected person's chromosomes), and age-related diseases, such as Warner's Syndrome (a rare illness that manifests rapid aging in younger people). The dynamics of telomere length have distinct patterns of expression in specific disease progressions. Therefore it has a great value in the prognosis of the diseases.
Telomere length can be measured by southern blot, hybridization protection assay, fluorescence in situ hybridization, flow cytometry, primed in situ, quantitative-polymerase chain reaction and single telomere length analysis.
Lack of telomerase activity and/or expression and short telomeres may cause dyskeratosis congenita, aplastic anemia, increase of death due to cardiovascular diseases, strokes or infections, hypertension or chronic stress.
It was shown that transduction of telomerase in telomerase knockout mice prevented damage in the liver.
In addition to the role of telomerase in telomere length maintenance, accumulating data suggest that the telomerase reverse transcriptase (TERT) protein has additional physiological functions, i.e. protecting cells and mice from various damages in a mechanism (yet unclear) that does not involve telomer elongation.
Compounds which activate telomerase will thus find application in multiple clinically relevant scenarios.